1. Field of the Invention
The present invention relates to a fuel controlling apparatus for an internal combustion engine provided with a fuel injector and, more particularly, to a fuel controlling apparatus for an internal combustion engine for transportation equipment, such as small planing boats, snowmobiles or motorcycles for motocross.
2. Description of the Related Art
FIG. 1 shows a small planing boat as an example of transportation equipment mounted with an internal combustion engine to which the present invention may be applied. The construction of a general small planing boat will be explained with reference to FIG. 1. The small planing boat has a body including a hull 1 and a deck 2. A saddle seat 3 and a handlebar 4 are supported on the deck 2. A water-jet propulsion unit 8 is disposed in a rear portion of the hull 1. The water-jet propulsion unit 8 includes a duct 9, guide vanes (current plates) 15, a jet nozzle 5 and an impeller 7. A laterally swingable steering nozzle 13 is disposed behind the jet nozzle 5. The impeller 7 is housed in the duct 9 and is mounted on an impeller shaft (drive shaft) 10. The impeller shaft 10 is coupled with the output shaft of an engine 11 supported on the hull 1. A rear end portion of the impeller shaft 10 is supported for rotation in a bearing housed in a bearing case 15a held on the guide vanes 15. When the impeller 7 is rotated, water is sucked through a water inlet 12 formed in the bottom of the hull 1 into the duct 9, flows through the guide vanes 15 and the jet nozzle 5 and is jetted out through the rear end opening 13a of the steering nozzle 13.
Generally speaking, an engine of transportation equipment may be provided with a carburetor. However, the engine 11 mounted on the small planing boat shown in FIG. 1 is provided with a fuel injector 14 because the fuel injector 14 enables precise fuel injection timing control.
The fuel injection operation of the engine 11 provided with the fuel injector 14 is controlled by, for example, an xcex1N control mode. The xcex1N control mode measures throttle opening xcex1 and engine speed N, selects an optimum injection quantity of fuel from a map stored beforehand in a controller on the basis of the values of throttle opening xcex1 and engine speed N, and adjusts the injection duration and the opening of the fuel injector. An overspeed limiting device prevents the operation of the engine at engine speeds exceeding an upper limit engine speed by cutting ignition and/or cutting down fuel.
Some times, it is difficult to determine an appropriate injection quantity for an air demand in an engine in case that fuel injection is controlled by xcex1N control, especially in case that fuel injection is controlled by xcex1N control and overspeed is limited by, for example, cutting ignition, because of the following reasons.
In most cases, the small planing boat planes over waves. The engine operates under no load when the water inlet 12 of the water jet propulsion unit 8 emerges from water and operates under load when the water inlet 12 is immersed in water. Consequently, no-load running and loaded running are repeated in a short time.
When the engine is controlled for overspeed limiting that cuts ignition, an engine speed repeatedly exceeds an upper limit engine speed at a high frequency in a short time due to the repetition of no-load running and loaded running while the small planing boat is planing over waves with the engine operating at engine speeds near the upper limit engine speed. Consequently, combustion and misfire are repeated. The repetition of combustion and misfire causes the pulsation of the exhaust and the variation of scavenging efficiency entailing the variation of air demand. However, it is difficult for xcex1N control to determine air demand accurately and hence it is difficult to set a fuel quantity properly.
An optimum air-fuel ratio can be determined by setting a fuel injection quantity for a measured air demand which is measured by an air flowmeter. However, the air flowmeter is expensive. Moreover, a valve type flowmeter is not preferable because the valve cover of the valve type flowmeter exerts resistance on intake air and the controllability of the engine is deteriorated.
Accordingly, it is an object of the present invention to stabilize combustion in an internal combustion engine provided with a fuel injector by properly injecting fuel according to air demand particularly while the internal combustion engine is operating at engine speeds near an upper limit engine speed and the actual engine speed frequently exceeds the upper limit engine speed.
According to one aspect of the present invention, a fuel controlling apparatus of an internal combustion engine for controlling a quantity of a fuel that is supplied to the engine includes a fuel injector that injects the fuel to the engine, the fuel injector being controlled on a basis of a throttle opening degree and an engine speed without measuring a quantity of an intake air that is taken through an intake system of the engine; and a carburetor that supplies the fuel to the engine using a negative pressure produced by the intake system of the engine. The fuel is supplied to the engine solely by the fuel injector while the engine speed is lower than a lower limit of a high engine speed range including an upper limit engine speed. The fuel is supplied to the engine by both the fuel injector and the carburetor so that the fuel of a necessary quantity is supplied to the engine by combining a quantity of the fuel supplied by the fuel injector and a quantity of the fuel supplied by the carburetor while the engine speed is in the high engine speed range.
Preferably, the lower limit of the high engine speed range varies in accordance with the throttle opening degree.
Preferably, the fuel controlling apparatus further includes an engine controller storing a map of an optimum fuel injection quantity as a function of the throttle opening degree and the engine speed. The fuel injector is controlled by the engine controller with reference to the map in accordance with the throttle opening degree and the engine speed.
Preferably, the carburetor does not operate in an entire range of the engine speed when the throttle opening degree is below about 50%.
Preferably, a ratio between the quantity of the fuel fed by the fuel injector and the quantity of the fuel fed by the carburetor is in a range of about 7:3 to about 5:5 when the throttle opening degree is 100%.
Preferably, the fuel controlling apparatus further includes an overspeed limiting device that stops or suppresses a combustion when the engine speed exceeds the upper limit engine speed.
Preferably, the carburetor is a piston type variable-venturi carburetor.
Preferably, the carburetor is an electromagnetic carburetor having a fuel jet nozzle controlled by a solenoid valve.